C-phy half-rate wire state encoder and decoder

ABSTRACT

Methods, apparatus, and systems provide improved throughput on a communication link. An apparatus has a plurality of line drivers, a first wire state encoder configured to receive a first symbol in a sequence of symbols when a 3-wire link is in a first signaling state, and to define a second signaling state for the 3-wire link based on the first symbol and the first signaling state, a second wire state encoder configured to receive a second symbol in the sequence of symbols, and to define a third signaling state for the 3-wire link based on the second symbol and the second signaling state. The first symbol immediately precedes the second symbol in the sequence of symbols. The 3-wire link transitions from the first to the second signaling state, and from the second to the third signaling state in consecutive transmission intervals.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.17/070,219 filed in the U.S. Patent Office on Oct. 14, 2020, whichclaimed priority to and the benefit of U.S. Provisional PatentApplication Ser. No. 62/927,524 filed in the U.S. Patent Office on Oct.29, 2019, the entire content of these applications being incorporatedherein by reference as if fully set forth below in their entirety andfor all applicable purposes.

TECHNICAL FIELD

The present disclosure relates generally to high-speed datacommunication interfaces, and more particularly, to improving datathroughput over a multi-wire, multi-phase data communication link.

BACKGROUND

Manufacturers of mobile devices, such as cellular phones, may obtaincomponents of the mobile devices from various sources, includingdifferent manufacturers. For example, an application processor in acellular phone may be obtained from a first manufacturer, while animaging device or camera may be obtained from a second manufacturer, anda display may be obtained from a third manufacturer. The applicationprocessor, the imaging device, the display controller, or other types ofdevice may be interconnected using a standards-based or proprietaryphysical interface. In one example, an imaging device may be connectedusing the Camera Serial Interface (CSI) defined by the Mobile IndustryProcessor Interface (MIPI) Alliance. In another example, a display mayinclude an interface that conforms to the Display Serial Interface (DSI)standard specified by the Mobile Industry Processor Interface (MIPI)Alliance.

A multiphase three-wire (C-PHY) interface defined by the MIPI Allianceuses a trio of conductors to transmit information between devices. Eachof the three wires may be in one of three signaling states duringtransmission of a symbol over the C-PHY interface. Clock information isencoded in a sequence of symbols transmitted on the C-PHY interface anda receiver generates a clock signal from transitions between consecutivesymbols. The maximum speed of the C-PHY interface and the ability of aclock and data recovery (CDR) circuit to recover clock information maybe limited by the maximum time variation related to transitions ofsignals transmitted on the different wires of the communication link,which can limit the number of symbols transmitted per second. Thecontinual increase in services and performance provided by mobiledevices has resulted in an ongoing demand for increased data throughputon multi-phase, multi-wire interfaces.

SUMMARY

Certain embodiments disclosed herein provide systems, methods andapparatus that enable improved communication on a multi-wire and/ormultiphase communication link through improved encoding techniques andprotocol. In some embodiments, data throughput is improved by increasingthe symbol clock rate used on the communication link. The communicationlink may be deployed in apparatus such as a mobile terminal havingmultiple Integrated Circuit (IC) devices.

In various aspects of the disclosure, a data communication apparatus hasa plurality of line drivers configured to couple the apparatus to a3-wire link, a first wire state encoder configured to receive a firstsymbol in a sequence of symbols when the 3-wire link is in a firstsignaling state, and to define a second signaling state for the 3-wirelink based on the first symbol and the first signaling state, a secondwire state encoder configured to receive a second symbol in the sequenceof symbols, and to define a third signaling state for the 3-wire linkbased on the second symbol and the second signaling state. The firstsymbol immediately precedes the second symbol in the sequence ofsymbols. The 3-wire link transitions from the first signaling state tothe second signaling state and from the second signaling state to thethird signaling state in consecutive symbol transmission intervals. Thesignaling states of at least one wire in the 3-wire link changes whenthe 3-wire link transitions from the second signaling state to the thirdsignaling state.

In one aspect, each of the first wire state encoder and the second wirestate encoder defines signaling states for the 3-wire link every twosymbol transmission intervals.

In certain aspects, the apparatus includes a clock generation circuitconfigured to provide a half-rate symbol clock signal that has a periodtwice the duration of each symbol transmission interval. The apparatusmay have a driver control circuit configured to control the plurality ofline drivers, and a multiplexer that selects between the secondsignaling state and the third signaling state to provide wire stateinformation to the driver control circuit. The multiplexer may selectbetween the second signaling state and the third signaling state basedon phase of the half-rate symbol clock signal. The apparatus may havefirst plurality of flipflops clocked by an inverse of the half-ratesymbol clock signal and configured to capture first control signalsrepresentative of the second signaling state, second plurality offlipflops clocked by the half-rate symbol clock signal and configured tocapture second control signals representative of the third signalingstate. The multiplexer may be further configured to provide the firstcontrol signals or the second control signals as the wire stateinformation.

In one aspect, the apparatus has one or more mappers configured to mapat least 16 bits of data to at least 7 symbols in the sequence ofsymbols. The 3-wire link may be operated in accordance with a C-PHYprotocol.

In one aspect, the apparatus has an equalizer circuit configured toreceive delayed versions of the second signaling state and the thirdsignaling state, and to configure the plurality of line drivers wheninitiating transmission of the third signaling state based ondifferences between the second signaling state and the third signalingstate.

In various aspects of the disclosure, a data communication methodincludes configuring a plurality of line drivers to couple the apparatusto a 3-wire link, receiving a first symbol in a sequence of symbols at afirst wire state encoder when the 3-wire link is in a first signalingstate, defining a second signaling state for the 3-wire link based onthe first symbol and the first signaling state, receiving a secondsymbol in the sequence of symbols at a second wire state encoder, anddefining a third signaling state for the 3-wire link based on the secondsymbol and the second signaling state. The first symbol immediatelyprecedes the second symbol in the sequence of symbols. The 3-wire linktransitions from the first signaling state to the second signaling stateand from the second signaling state to the third signaling state inconsecutive symbol transmission intervals. Signaling state of at leastone wire in the 3-wire link changes when the 3-wire link transitionsfrom the second signaling state to the third signaling state.

In various aspects of the disclosure, a processor-readable storagemedium includes code for configuring a plurality of line drivers tocouple the apparatus to a 3-wire link, receiving a first symbol in asequence of symbols at a first wire state encoder when the 3-wire linkis in a first signaling state, defining a second signaling state for the3-wire link based on the first symbol and the first signaling state,receiving a second symbol in the sequence of symbols at a second wirestate encoder, and defining a third signaling state for the 3-wire linkbased on the second symbol and the second signaling state. The firstsymbol immediately precedes the second symbol in the sequence ofsymbols. The 3-wire link transitions from the first signaling state tothe second signaling state and from the second signaling state to thethird signaling state in consecutive symbol transmission intervals.Signaling states of at least one wire in the 3-wire link changes whenthe 3-wire link transitions from the second signaling state to the thirdsignaling state.

In various aspects of the disclosure, a data communication apparatus,has a plurality of receivers configured to provide difference signalsrepresentative of differences in signaling state between each pair ofwires in a 3-wire link, a first wire state decoder configured to providea first symbol based on differences between state of the differencesignals in a first half-cycle of a symbol clock and state of thedifference signals in a second half-cycle of the symbol clock thatimmediately precedes the first half-cycle in the symbol clock, a secondwire state decoder configured to provide a second symbol based ondifferences between the state of the difference signals in the secondhalf-cycle of the symbol clock and state of the difference signals in athird half-cycle of the symbol clock that immediately precedes thesecond half-cycle in the symbol clock, and a demapper configured todecode data from a sequence of symbols that includes the first symboland the second symbol. The first symbol immediately precedes the secondsymbol in the sequence of symbols.

In some aspects, signaling state of at least one difference signalchanges at each transition between half-cycles of the half-rate symbolclock. The apparatus may include a clock recovery circuit configured toderive the symbol clock from the difference signals.

In certain aspects, the apparatus includes a plurality of differencesignal processors. Each difference signal processor is coupled to anassociated difference signal. Each difference signal processor may beconfigured to provide a first signal representing the state of thecorresponding difference signal in the first half-cycle of the symbolclock, a second signal representing the state of the correspondingdifference signal in the second half-cycle of the symbol clock, and athird signal representing the state of the corresponding differencesignal in the third half-cycle of the symbol clock.

In one aspect, the demapper is further configured to decode a 16-bitword from each of a plurality of sequences of seven symbols or decode a32-bit word from each pair of sequences of seven symbols generatedconcurrently by the first wire state decoder and the second wire statedecoder. The 3-wire link may be operated in accordance with a C-PHYprotocol.

In various aspects of the disclosure, a data communication methodincludes providing difference signals representative of differences insignaling state between each pair of wires in a 3-wire link, providing afirst symbol based on differences between state of the differencesignals in a first half-cycle of a symbol clock and state of thedifference signals in a second half-cycle of the symbol clock thatimmediately precedes the first half-cycle in the symbol clock, providinga second symbol based on differences between the state of the differencesignals in the second half-cycle of the symbol clock and state of thedifference signals in a third half-cycle of the symbol clock thatimmediately precedes the second half-cycle in the symbol clock, anddecoding data from a sequence of symbols that includes the first symboland the second symbol. The first symbol may immediately precede thesecond symbol in the sequence of symbols.

In various aspects of the disclosure, includes code for providingdifference signals representative of differences in signaling statebetween each pair of wires in a 3-wire link, providing a first symbolbased on differences between state of the difference signals in a firsthalf-cycle of a symbol clock and state of the difference signals in asecond half-cycle of the symbol clock that immediately precedes thefirst half-cycle in the symbol clock, providing a second symbol based ondifferences between the state of the difference signals in the secondhalf-cycle of the symbol clock and state of the difference signals in athird half-cycle of the symbol clock that immediately precedes thesecond half-cycle in the symbol clock, and decoding data from a sequenceof symbols that includes the first symbol and the second symbol. Thefirst symbol may immediately precede the second symbol in the sequenceof symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an apparatus employing a data link between IC devicesthat is selectively operated according to one of a plurality ofavailable standards or protocols, which may include a C-PHY protocol.

FIG. 2 illustrates a system architecture for an apparatus employing adata link between IC devices that selectively operates according to oneof plurality of available standards.

FIG. 3 illustrates a C-PHY 3-phase transmitter.

FIG. 4 illustrates signaling in a C-PHY 3-phase encoded interface.

FIG. 5 illustrates a C-PHY 3-phase receiver.

FIG. 6 is a state diagram illustrating potential state transitions in aC-PHY 3-phase encoded interface.

FIG. 7 illustrates one example of encoding in a C-PHY 3-phasetransmitter.

FIG. 8 illustrates one example of decoding in a C-PHY 3-phase receiver.

FIG. 9 illustrates examples of mapping circuits implemented with a dualpath architecture in accordance aspects of the disclosure.

FIG. 10 illustrates a first example of a transmitter configured to use ahalf-rate symbol clock signal to encode input data for a C-PHY interfacein accordance with certain aspects disclosed herein.

FIG. 11 illustrates an example of timing for the transmitter illustratedin FIG. 10.

FIG. 12 illustrates a second example of a transmitter configured to usea half-rate symbol clock signal to encode input data for a C-PHYinterface in accordance with certain aspects disclosed herein.

FIG. 13 illustrates difference signal processors that may be used in areceiver configured for half-rate symbol clock operation in accordancewith certain aspects of this disclosure.

FIG. 14 illustrates a receiver circuit configured to use a half-ratesymbol clock signal to decode data from signaling state of a C-PHY busin accordance with certain aspects disclosed herein.

FIG. 15 illustrates timing associated with the receiver illustrated inFIG. 14.

FIG. 16 illustrates examples of demapping circuits implemented with adual path architecture in accordance aspects of the disclosure.

FIG. 17 illustrates an example of an apparatus employing a processingcircuit that may be adapted according to certain aspects disclosedherein.

FIG. 18 is a flow chart of a method performed at a transmitter accordingto certain aspects disclosed herein.

FIG. 19 is a diagram illustrating an example of a hardwareimplementation for a receiving apparatus in accordance with certainaspects disclosed herein.

FIG. 20 is a flow chart of a method performed at a receiver according tocertain aspects disclosed herein.

FIG. 21 is a diagram illustrating an example of a hardwareimplementation for a receiving apparatus in accordance with certainaspects disclosed herein.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well-known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

As used in this application, the terms “component,” “module,” “system”and the like are intended to include a computer-related entity, such as,but not limited to hardware, firmware, a combination of hardware andsoftware, software, or software in execution. For example, a componentmay be, but is not limited to being, a process running on a processor, aprocessor, an object, an executable, a thread of execution, a programand/or a computer. By way of illustration, both an application runningon a computing device and the computing device can be a component. Oneor more components can reside within a process and/or thread ofexecution and a component may be localized on one computer and/ordistributed between two or more computers. In addition, these componentscan execute from various processor-readable media having various datastructures stored thereon. The components may communicate by way oflocal and/or remote processes such as in accordance with a signal havingone or more data packets, such as data from one component interactingwith another component in a local system, distributed system, and/oracross a network such as the Internet with other systems by way of thesignal.

Moreover, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or.” That is, unless specified otherwise, or clearfrom the context, the phrase “X employs A or B” is intended to mean anyof the natural inclusive permutations. That is, the phrase “X employs Aor B” is satisfied by any of the following instances: X employs A; Xemploys B; or X employs both A and B. In addition, the articles “a” and“an” as used in this application and the appended claims shouldgenerally be construed to mean “one or more” unless specified otherwiseor clear from the context to be directed to a singular form.

Overview

Certain aspects of the invention may be applicable to improving a C-PHYinterface specified by the MIPI Alliance, which is often deployed toconnect electronic devices that are subcomponents of a mobile apparatussuch as a telephone, a mobile computing device, an appliance, automobileelectronics, avionics systems, etc. Examples of a mobile apparatusinclude a cellular phone, a smart phone, a session initiation protocol(SIP) phone, a laptop, a notebook, a netbook, a smartbook, a personaldigital assistant (PDA), a satellite radio, a global positioning system(GPS) device, a multimedia device, a video device, a digital audioplayer (e.g., MP3 player), a camera, a game console, a wearablecomputing device (e.g., a smartwatch, a health or fitness tracker,etc.), an appliance, a sensor, a vending machine, or any other similarlyfunctioning device.

Certain aspects disclosed herein enable devices to communicate at higherdata rates over a three-wire communication link than possible usingconventional C-PHY symbol rates. In various aspects of the disclosure, adata communication apparatus has a plurality of line drivers configuredto couple the apparatus to a 3-wire link, and a data encoder configuredto encode at least 4 bits of binary data in each transition between twosymbols that are consecutively transmitted by the plurality of linedrivers over the 3-wire link such that each pair ofconsecutively-transmitted symbols includes two different symbols. Eachsymbol defines signaling states of the 3-wire link during an associatedsymbol transmission interval such that each wire of the 3-wire link isin a different signaling state from the other wires of the of the 3-wirelink during the associated symbol transmission interval. Data may beencoded using a combination of 3-phase and pulse amplitude modulation.The apparatus may include a wire state encoder configured to receive asequence of symbols from the data encoder, and provide control signalsto the plurality of line drivers. The control signals cause each of theplurality of line drivers to drive one wire of the 3-wire link to asignaling state defined by each symbol during a symbol transmissioninterval provided for each symbol in the sequence of symbols.

The C-PHY interface is a high-speed serial interface that can providehigh throughput over bandwidth-limited channels. The C-PHY interface maybe deployed to connect application processors to peripherals, includingdisplays and cameras. The C-PHY interface encodes data into symbols thatare transmitted in a three-phase signal over a set of three wires, whichmay be referred to as a trio, or as a trio of wires. The three-phasesignal is transmitted on each wire of the trio in different phases. Eachthree-wire trio provides a lane on a communication link. A symbolinterval may be defined as the interval of time in which a single symbolcontrols the signaling state of a trio. In each symbol interval, onewire is undriven or is driven to an intermediate voltage state while theremaining two of the three wires are differentially driven such that oneof the two differentially driven wires assumes a first voltage level andthe other differentially driven wire assumes to a second voltage leveldifferent from the first voltage level. The undriven wire may float,and/or be terminated such that it assumes a third voltage level that isat or near the intermediate voltage level, which may be a mid-levelvoltage level between the first and second voltage levels. In oneexample, the driven voltage levels may be +V and −V with the thirdvoltage being 0 Volts. In another example, the driven voltage levels maybe +V and 0 Volts with the undriven voltage being +V/2. Differentsymbols are transmitted in each consecutively transmitted pair ofsymbols, and different pairs of wires may be differentially driven indifferent symbol intervals.

FIG. 1 depicts an example of apparatus 100 that may employ C-PHY 3-phaseprotocols to implement one or more communication links. The apparatus100 may include an SoC a processing circuit 102 having multiple circuitsor devices 104, 106 and/or 108, which may be implemented in one or moreASICs or in an SoC. In one example, the apparatus 100 may be acommunication device and the processing circuit 102 may include aprocessing device provided in an ASIC 104, one or more peripheraldevices 106, and a transceiver 108 that enables the apparatus tocommunicate through an antenna 124 with a radio access network, a coreaccess network, the Internet and/or another network.

The ASIC 104 may have one or more processors 112, one or more modems110, on-board memory 114, a bus interface circuit 116 and/or other logiccircuits or functions. The processing circuit 102 may be controlled byan operating system that may provide an application programminginterface (API) layer that enables the one or more processors 112 toexecute software modules residing in the on-board memory 114 or otherprocessor-readable storage 122 provided on the processing circuit 102.The software modules may include instructions and data stored in theon-board memory 114 or processor-readable storage 122. The ASIC 104 mayaccess its on-board memory 114, the processor-readable storage 122,and/or storage external to the processing circuit 102. The on-boardmemory 114, the processor-readable storage 122 may include read-onlymemory (ROM) or random-access memory (RAM), electrically erasableprogrammable ROM (EEPROM), flash cards, or any memory device that can beused in processing systems and computing platforms. The processingcircuit 102 may include, implement, or have access to a local databaseor other parameter storage that can maintain operational parameters andother information used to configure and operate the apparatus 100 and/orthe processing circuit 102. The local database may be implemented usingregisters, a database module, flash memory, magnetic media, EEPROM, softor hard disk, or the like. The processing circuit 102 may also beoperably coupled to external devices such as the antenna 124, a display126, operator controls, such as switches or buttons 128, 130 and/or anintegrated or external keypad 132, among other components. A userinterface module may be configured to operate with the display 126,external keypad 132, etc. through a dedicated communication link orthrough one or more serial data interconnects.

The processing circuit 102 may provide one or more buses 118 a, 118 b,120 that enable certain devices 104, 106, and/or 108 to communicate. Inone example, the ASIC 104 may include a bus interface circuit 116 thatincludes a combination of circuits, counters, timers, control logic andother configurable circuits or modules. In one example, the businterface circuit 116 may be configured to operate in accordance withcommunication specifications or protocols. The processing circuit 102may include or control a power management function that configures andmanages the operation of the apparatus 100.

FIG. 2 illustrates certain aspects of an apparatus 200 that includes aplurality of IC devices 202 and 230, which can exchange data and controlinformation through a communication link 220. The communication link 220may be used to connect a pair of IC devices 202 and 230 that are locatedin close proximity to one another, or that are physically located indifferent parts of the apparatus 200. In one example, the communicationlink 220 may be provided on a chip carrier, substrate or circuit boardthat carries the IC devices 202 and 230. In another example, a first ICdevice 202 may be located in a keypad section of a flip-phone while asecond IC device 230 may be located in a display section of theflip-phone. In another example, a portion of the communication link 220may include a cable or optical connection.

The communication link 220 may include multiple channels 222, 224 and226. One or more channel 226 may be bidirectional, and may operate inhalf-duplex and/or full-duplex modes. One or more channel 222 and 224may be unidirectional. The communication link 220 may be asymmetrical,providing higher bandwidth in one direction. In one example describedherein, a first channel 222 may be referred to as a forward channel 222while a second channel 224 may be referred to as a reverse channel 224.The first IC device 202 may be designated as a host system ortransmitter, while the second IC device 230 may be designated as aclient system or receiver, even if both IC devices 202 and 230 areconfigured to transmit and receive on the channel 222. In one example,the forward channel 222 may operate at a higher data rate whencommunicating data from a first IC device 202 to a second IC device 230,while the reverse channel 224 may operate at a lower data rate whencommunicating data from the second IC device 230 to the first IC device202.

The IC devices 202 and 230 may each include a processor 206, 236 orother processing and/or computing circuit or device. In one example, thefirst IC device 202 may perform core functions of the apparatus 200,including establishing and maintaining wireless communication through awireless transceiver 204 and an antenna 214, while the second IC device230 may support a user interface that manages or operates a displaycontroller 232, and may control operations of a camera or video inputdevice using a camera controller 234. Other features supported by one ormore of the IC devices 202 and 230 may include a keyboard, avoice-recognition component, and other input or output devices. Thedisplay controller 232 may include circuits and software drivers thatsupport displays such as a liquid crystal display (LCD) panel,touch-screen display, indicators and so on. The storage media 208 and238 may include transitory and/or non-transitory storage devices adaptedto maintain instructions and data used by respective processors 206 and236, and/or other components of the IC devices 202 and 230.Communication between each processor 206, 236 and its correspondingstorage media 208 and 238 and other modules and circuits may befacilitated by one or more internal bus 212 and 242 and/or a channel222, 224 and/or 226 of the communication link 220.

The reverse channel 224 may be operated in the same manner as theforward channel 222, and the forward channel 222 and the reverse channel224 may be capable of transmitting at comparable speeds or at differentspeeds, where speed may be expressed as data transfer rate, symboltransmission rate and/or clocking rates. The forward and reverse datarates may be substantially the same or may differ by orders ofmagnitude, depending on the application. In some applications, a singlebidirectional channel 226 may support communication between the first ICdevice 202 and the second IC device 230. The forward channel 222 and/orthe reverse channel 224 may be configurable to operate in abidirectional mode when, for example, the forward and reverse channels222 and 224 share the same physical connections and operate in ahalf-duplex manner. In one example, the communication link 220 may beoperated to communicate control, command and other information betweenthe first IC device 202 and the second IC device 230 in accordance withan industry or other standard.

The communication link 220 of FIG. 2 may be implemented according toMIPI Alliance specifications for C-PHY and may provide a wired bus thatincludes a plurality of signal wires (denoted as M wires). The M wiresmay be configured to carry N-phase encoded data in a high-speed digitalinterface, such as a mobile display digital interface (MDDI). The Mwires may facilitate N-phase polarity encoding on one or more of thechannels 222, 224 and 226. The physical layer drivers 210 and 240 may beconfigured or adapted to generate N-phase polarity encoded data fortransmission on the communication link 220. The use of N-phase polarityencoding provides high speed data transfer and may consume half or lessof the power of other interfaces because fewer drivers are active inN-phase polarity encoded data links.

The physical layer drivers 210 and 240 can typically encode multiplebits per transition on the communication link 220 when configured forN-phase polarity encoding. In one example, a combination of 3-phaseencoding and polarity encoding may be used to support a wide videographics array (WVGA) 80 frames per second LCD driver IC without a framebuffer, delivering pixel data at 810 Mbps for display refresh.

FIG. 3 is a diagram 300 illustrating a 3-wire, 3-phase polarity encoderthat may be used to implement certain aspects of the communication link220 depicted in FIG. 2. The example of 3-wire, 3-phase encoding isselected solely for the purpose of simplifying descriptions of certainaspects of the invention. The principles and techniques disclosed for3-wire, 3-phase encoders can be applied in other configurations ofM-wire, N-phase polarity encoders.

Signaling states defined for each of the 3 wires in a 3-wire, 3-phasepolarity encoding scheme may include a positively driven state, anegatively driven state and an intermediate or undriven state. Thepositively driven state and the negatively driven state may be obtainedby providing a voltage differential between two of the signal wires 318a, 318 b and/or 318 c, and/or by driving a current through two of thesignal wires 318 a, 318 b and/or 318 c connected in series such that thecurrent flows in different directions in the two signal wires 318 a, 318b and/or 318 c. A third state may be provided as an undriven staterealized by placing an output of a driver of a signal wire 318 a, 318 bor 318 c in a high-impedance mode. Typically, there is no significantcurrent flow through an undriven signal wire 318 a, 318 b or 318 c.Alternatively, or additionally, the third state may be an intermediatestate obtained on a signal wire 318 a, 318 b or 318 c by passively oractively causing one signal wire 318 a, 318 b or 318 c to attain avoltage level that lies substantially halfway between positive andnegative voltage levels provided on driven signal wires 318 a, 318 band/or 318 c. Signaling states defined for a 3-wire, 3-phase polarityencoding scheme may be denoted using the three voltage or current states(+1, −1, and 0).

A 3-wire, 3-phase polarity encoder may employ line drivers 308 tocontrol the signaling state of signal wires 318 a, 318 b and 318 c. Theline drivers 308 may be implemented as unit-level current-mode orvoltage-mode drivers. In some implementations, each line driver 308 mayreceive sets of signals 316 a, 316 b and 316 c that determine the outputstate of corresponding signal wires 318 a, 318 b and 318 c. In oneexample, each of the sets of signals 316 a, 316 b and 316 c may includetwo or more signals, including a pull-up signal (PU signal) and apull-down signal (PD signal) that, when high, activate pull-up and pulldown circuits that drive the signal wires 318 a, 318 b and 318 c towarda higher level or lower level voltage, respectively. In this example,when both the PU signal and the PD signal are low, the signal wires 318a, 318 b and 318 c may be terminated to a mid-level voltage.

For each transmitted symbol interval in an 3-wire, 3-phase polarityencoding scheme, at least one signal wire 318 a, 318 b or 318 c is inthe midlevel/undriven (0) voltage or current state, while the number ofpositively driven (+1 voltage or current state) signal wires 318 a, 318b or 318 c is equal to the number of negatively driven (−1 voltage orcurrent state) signal wires 318 a, 318 b or 318 c, such that the sum ofcurrent flowing to the receiver is always zero. For each symbol, thesignaling state of at least one signal wire 318 a, 318 b or 318 c ischanged from the wire state transmitted in the preceding transmissioninterval.

In operation, a mapper 302 may receive and map 16-bit data 310 to 7symbols 312. In the C-PHY example, each of the 7 symbols defines thestates of the signal wires 318 a, 318 b and 318 c for one symbolinterval. The 7 symbols 312 may be serialized using parallel-to-serialconverters 304 that provide a timed sequence of symbols 314 for eachsignal wire 318 a, 318 b and 318 c. The sequence of symbols 314 istypically timed using a transmission clock. A 3-wire, 3-phase encoder306 receives the sequence of 7 symbols 314 produced by the mapper onesymbol at a time and computes the state of each signal wire 318 a, 318 band 318 c for each symbol interval. The 3-wire, 3-phase encoder 306selects the states of the signal wires 318 a, 318 b and 318 c based onthe current input symbol 14 and the previous states of signal wires 318a, 318 b and 318 c.

The use of 3-wire, 3-phase encoding permits a number of bits to beencoded in a plurality of symbols where the bits per symbol is not aninteger. In the example of a C-PHY communication link, there are 3available combinations of 2 wires, which may be driven simultaneously,and 2 possible combinations of polarity on the pair of wires that isdriven, yielding 6 possible states. Since each transition occurs from acurrent state, 5 of the 6 states are available at every transition. Thestate of at least one wire is required to change at each transition.With 5 states, log₂(5)≅2.32 bits may be encoded per symbol. Accordingly,a mapper may accept a 16-bit word and convert it to 7 symbols because 7symbols carrying 2.32 bits per symbol can encode 16.24 bits. In otherwords, a combination of seven symbols that encode five states has 5⁷(78,125) permutations. Accordingly, the 7 symbols may be used to encodethe 2¹⁶ (65,536) permutations of 16 bits.

FIG. 4 includes an example of a timing chart 400 for signals encodedusing a three-phase modulation data-encoding scheme, which is based onthe circular state diagram 450. Information may be encoded in a sequenceof signaling states where, for example, a wire or connector is in one ofthree phase states S₁, S₂ and S₃ defined by the circular state diagram450. Each state may be separated from the other states by a 120° phaseshift. In one example, data may be encoded in the direction of rotationof phase states on the wire or connector. The phase states in a signalmay rotate in clockwise direction 452 and 452′ or counterclockwisedirection 454 and 454′. In the clockwise direction 452 and 452′ forexample, the phase states may advance in a sequence that includes one ormore of the transitions from S₁ to S₂, from S₂ to S₃ and from S₃ to S₁.In the counterclockwise direction 454 and 454′, the phase states mayadvance in a sequence that includes one or more of the transitions fromS₁ to S₃ from S₃ to S₂ and from S₂ to S₁. The three signal wires 318 a,318 b and 318 c carry different versions of the same signal, where theversions may be phase shifted by 120° with respect to one another. Eachsignaling state may be represented as a different voltage level on awire or connector and/or a direction of current flow through the wire orconnector. During each of the sequence of signaling states in a 3-wiresystem, each signal wire 318 a, 318 b and 318 c is in a differentsignaling states than the other wires. When more than 3 signal wires 318a, 318 b and 318 c are used in a 3-phase encoding system, two or moresignal wires 318 a, 318 b and/or 318 c can be in the same signalingstate at each signaling interval, although each state is present on atleast one signal wire 318 a, 318 b and/or 318 c in every signalinginterval.

Information may be encoded in the direction of rotation at each phasetransition 410, and the 3-phase signal may change direction for eachsignaling state. Direction of rotation may be determined by consideringwhich signal wires 318 a, 318 b and/or 318 c are in the ‘0’ state beforeand after a phase transition, because the undriven signal wire 318 a,318 b and/or 318 c changes at every signaling state in a rotatingthree-phase signal, regardless of the direction of rotation.

The encoding scheme may also encode information in the polarity 408 ofthe two signal wires 318 a, 318 b and/or 318 c that are actively driven.At any time in a 3-wire implementation, exactly two of the signal wires318 a, 318 b, 318 c are driven with currents in opposite directionsand/or with a voltage differential. In one implementation, data may beencoded using two bit values 412, where one bit is encoded in thedirection of phase transitions 410 and the second bit is encoded in thepolarity 408 for the current state.

The timing chart 400 illustrates data encoding using both phase rotationdirection and polarity. The curves 402, 404 and 406 relate to signalscarried on three signal wires 318 a, 318 b and 318 c, respectively formultiple phase states. Initially, the phase transitions 410 are in aclockwise direction and the most significant bit is set to binary ‘1,’until the rotation of phase transitions 410 switches at a time 414 to acounterclockwise direction, as represented by a binary ‘0’ of the mostsignificant bit. The least significant bit reflects the polarity 408 ofthe signal in each state.

According to certain aspects disclosed herein, one bit of data may beencoded in the rotation, or phase change in a 3-wire, 3-phase encodingsystem, and an additional bit may be encoded in the polarity of the twodriven wires. Additional information may be encoded in each transitionof a 3-wire, 3-phase encoding system by allowing transition to any ofthe possible states from a current state. Given rotational phases andtwo polarities for each phase, 6 states are available in a 3-wire,3-phase encoding system. Accordingly, 5 states are available from anycurrent state, and there may be log₂(5)≅2.32 bits encoded per symbol(transition), which allows the mapper 302 to accept a 16-bit word andencode it in 7 symbols.

FIG. 5 is a diagram illustrating certain aspects of a 3-wire, 3-phasedecoder 500. Differential receivers 502 a, 502 b, 502 c and a wire statedecoder 504 are configured to provide a digital representation of thestate of the three transmission lines (e.g., the signal wires 318 a, 318b and 318 c illustrated in FIG. 3), with respect to one another, and todetect changes in the state of the three transmission lines compared tothe state transmitted in the previous symbol period. Seven consecutivestates are assembled by the serial-to-parallel convertors 506 to obtaina set of 7 symbols 516 to be processed by the demapper 508. The demapper508 produces 16 bits of data 518 that may be buffered in afirst-in-first-out (FIFO) register 510 to provide output data 520.

The wire state decoder 504 may extract a sequence of symbols 514 fromphase encoded signals received on the signal wires 318 a, 318 b and 318c. The symbols 514 are encoded as a combination of phase rotation andpolarity as disclosed herein. The wire state decoder may include a CDRcircuit 524 that extracts a clock 526 that can be used to reliablycapture wire states from the signal wires 318 a, 318 b and 318 c. Atransition occurs on least one of the signal wires 318 a, 318 b and 318c at each symbol boundary and the CDR circuit 524 may be configured togenerate the clock 526 based on the occurrence of a transition ormultiple transitions. An edge of the clock may be delayed to allow timefor all signal wires 318 a, 318 b and 318 c to have stabilized and tothereby ensure that the current wire state is captured for decodingpurposes.

FIG. 6 is state diagram 600 illustrating the possible signaling states602, 604, 606, 612, 614, 616 of the three wires, with the possibletransitions illustrated from each state. In the example of a 3-wire,3-phase communication link, 6 states and 30 state transitions areavailable. The possible signaling states 602, 604, 606, 612, 614 and 616in the state diagram 600 include and expand on the states shown in thecircular state diagram 450 of FIG. 4. As shown in the exemplar of astate element 628, each signaling state 602, 604, 606, 612, 614 and 616in the state diagram 600 defines voltage signaling state of the signalwires 318 a, 318 b, 318 c, which are labeled A, B and C respectively.For example, in signaling state 602 (+x) wire A=+1, wire B=−1 and wireC=0, yielding output of differential receiver 502 a (A−B)=+2,differential receiver 502 b (B−C)=−1 and differential receiver 502 c(C−A)=−1. Transition decisions taken by phase change detect circuits ina receiver are based on 5 possible levels produced by the differentialreceivers 502 a, 502 b, 502 c, which include −2, −1, 0, +1 and +2voltage states.

The transitions in the state diagram 600 can be represented by a Flip,Rotate, Polarity symbol (e.g., the FRP symbol 626) that has one of thethree-bit binary values in the set: {000, 001, 010, 011, 100}. TheRotation bit 622 of the FRP symbol 626 indicates the direction of phaserotation associated with a transition to a next state. The Polarity bit624 of the FRP symbol 626 is set to binary 1 when a transition to a nextstate involves a change in polarity. When the Flip bit 620 of the FRPsymbol 626 is set to binary 1, the Rotate and Polarity values may beignored and/or zeroed. A flip represents a state transition thatinvolves only a change in polarity. Accordingly, the phase of a 3-phasesignal is not considered to be rotating when a flip occurs, and thepolarity bit is redundant when a flip occurs. The FRP symbol 626corresponds to wire state changes for each transition. The state diagram600 may be separated into an inner circle 608 that includes the positivepolarity signaling states 602, 604, 606 and an outer circle 618 thatencompasses the negative polarity signaling states 612, 614, 616.

FIG. 7 illustrates an example of wire state encoding 700 that may beused in certain C-PHY interfaces. A symbol encoder 702 receives a streamof FRP symbols 708 that may have the format of the FRP symbol 626illustrated in FIG. 6. A mapper 302 (see FIG. 3) may generate the streamof FRP symbols 708 from data to be communicated over a C-PHY bus. Thesymbol encoder 702 provides a current transmit symbol 714 for each FRPsymbol in the stream of FRP symbols 708 based on the immediatelypreceding transmit symbol 716. The immediately preceding transmit symbol716 is maintained by flipflops or a register 706 configured to capturethe current transmit symbol 714 based on timing provided by a symbolclock signal 710. The symbol clock signal 710 also provides timing forpre-drive and control circuit 704, which controls the operation of linedrivers coupled to the C-PHY bus. In some instances, the pre-drive andcontrol circuit 704 may capture and hold the current transmit symbol 714for the duration of a cycle of the symbol clock signal 710. In someinstances, the pre-drive and control circuit 704 may provide a set ofsignals 712 that control pull-up and pull-down sections of the linedriver circuit. The table 720 illustrates the state of the set ofsignals 712 that produce the voltage levels 724 for each wire state 722defined for the C-PHY bus.

FIG. 8 illustrates an example of wire state decoding 800 that may beused in certain C-PHY interfaces. A set of comparators 802 monitorssignaling state 822 of the C-PHY bus and produces difference signalsthat are captured as current wire state 826 by first flipflops orregisters 804 based on timing provided by a symbol clock signal 820. Aclock recovery circuit 812 monitors signaling state 822 of the C-PHY busand produces a receive clock signal 828 that may be gated by gatinglogic 816 to produce the symbol clock signal 820. The gating logic 816may receive an enable signal 830 from clock window logic 814 and thegating logic 816 provides the symbol clock signal 820 when a settlesignal 818 indicates that the receive clock signal 828 is valid. Secondflipflops or registers 806 provide the previous wire state 824 bycapturing the current wire state 826 based on timing provided by thesymbol clock signal 820.

A symbol decoder 808 produces a stream of FRP symbols 810 that may havethe format of the FRP symbol 626 illustrated in FIG. 6. The stream ofFRP symbols 810 may be provided to a demapper 508 (see FIG. 5) thatdecodes data from the stream of FRP symbols 810. The symbol decoder 808produces each FRP symbol in the stream of FRP symbols 810 based ondifferences between previous wire state 824 and current wire state 826.

Increasing complexity and performance of application and sensors hasproduced corresponding increased demands for data rates and throughput.For example, increased resolution of imaging devices and imaging devicecan be expected to produce ever-increasing volumes of image data to becommunicated over a C-PHY bus between application processors and otherdevices. Demand for higher frame rates and the provision of multipleimaging devices in an apparatus also multiply the volumes of image datato be transmitted and can reduce the time available to transmit theimage data. Display systems are being concurrently provided withincreased resolution and may be required to handle increased framerates. The increased demand for throughput can be difficult to meetusing a conventional C-PHY interface.

The C-PHY data path operates at full rate clock, whereby data istransmitted and sampled on a single type of edge of the transmitter'ssymbol clock signal or receiver's symbol clock signal respectively. Thetype of edge used for timing in a symbol clock signal may be the risingedge or the falling edge, based on the circuit design employed in animplementation. Data throughput is determined by the symbol rate of theC-PHY interface, where symbol rate may be expressed as the number ofsymbols transmitted per second over the C-PHY bus. According toconventional C-PHY specifications:

Symbol rate=Symbol clock frequency.

Data throughput may be measured as the number of bits per secondtransmitted over the C-PHY bus. In one example, approximately 2.32 bitscan be encoded in the transitions between consecutively-transmittedsymbols, such that

Data  throughput = 2.32 * (Symbol  clock  frequency).

Increased data throughput can be obtained by increasing the symbol clockfrequency. The ability to increase symbol clock frequency is limited bythe performance of circuits in C-PHY transmitters and receivers. In manyimplementations, switching time defined for logic gates may limit themaximum symbol clock frequency, and/or may limit the number of levels ofgates in circuits that operate at symbol clock frequency. In oneexample, differences in propagation time through logic circuits of areceiver can limit the time interval in which a symbol can be reliablysampled. In another example, generation and distribution of a high-speedfull-rate symbol clock signal may be difficult to accomplish and maycomplicate integrated circuit design.

A C-PHY interface implemented in accordance with certain aspects of thisdisclosure can increase data throughput for a C-PHY interface withoutincreasing the symbol clock rate. In one aspect, timing in a C-PHY datapath may controlled by a half-rate symbol clock signal. Symbols can betransmitted on both rising and falling edges of the symbol clock signalwhen a half-rate symbol clock signal is used, relaxing the frequencyrequirement for the symbol clock signal at higher symbol rates. The useof a half-rate symbol clock signal in accordance with certain aspects ofthis disclosure provides that:

Symbol  rate = 2 * (Symbol  clock  frequency).

Data throughput is measured as the number of bits per second transmittedover the C-PHY bus. When 2.32 bits are encoded in the transitionsbetween consecutively-transmitted symbols:

Data  throughput = 4.64 * (Symbol  clock  frequency).

In one example, the data throughput obtained using a 10 GHz symbol clocksignal in a conventional C-PHY interface can be obtained using a 5 GHzsymbol clock signal in a C-PHY interface implemented in accordance withcertain aspects of this disclosure.

Certain aspects of this disclosure relate to the structure andconfiguration of C-PHY transmitters and receivers that can operate usinghalf-rate symbol clock signals. In various examples, the C-PHYtransmitters and receivers are configured for a dual path architecture,each path encoding or decoding alternate symbols in a sequence ofsymbols. For the purposes of this description, the paths in atransmitter or receiver configured for use with a half-rate symbol clockare designated as odd and even paths. In one example, the odd path in atransmitter or receiver handles the symbols in a sequence that aretransmitted first, third, fifth symbols and so on, and the even path ina transmitter or receiver handles the symbols in a sequence that aretransmitted second, fourth, sixth symbols and so on. In operation, thepaths are symmetric in structure, and symbols or paths may bearbitrarily designated as odd and even. According to one aspect, a C-PHYtransmitter that is implemented with a dual path architecture includes amapper that provides odd and even symbols to corresponding odd and evenpaths. According to one aspect, a C-PHY receiver that is implementedwith a dual path architecture includes a demapper that receives odd andeven symbols from corresponding odd and even paths and interleaves theodd and even symbols to provide a sequence of symbols for decoding.

FIG. 9 illustrates examples of mapping circuits 900, 930 that may beimplemented in C-PHY transmitters configured with a dual patharchitecture in accordance aspects of the disclosure. The first mappingcircuit 900 includes two mappers 902, 904, each mapper 902, 904 feedingone of the paths in a transmitter, where the transmitter is implementedwith an even symbol path and an odd symbol path. Each even symboldefines a signaling state that is immediately followed by a signalingstate defined by an odd symbol and each odd symbol defines a signalingstate that is immediately followed by a signaling state defined by aneven symbol.

The first mapping circuit 900 may receive input data 912 as two 16-bitwords or as a single 32-bit word. The first mapping circuit 900 splits32-bit words into two 16-bit words. Each 16-bit word can be mapped intoa sequence of 7 FRP symbols by respective mappers 902, 904. Each 21-bitrepresentation of the sequence of 7 FRP symbols may be serialized toobtain a timed sequence of FRP symbols using respective serializers 906,908. The serializers 906, 908 provide one symbol per clock cycle of ahalf-rate symbol clock signal 910, which has a frequency equal to halfthe desired symbol transmission rate. In the illustrated example, twomappers 902, 904 provide a sequence of seven 3-bit FRP symbols tocorresponding serializers 906, 908.

Timing of the mappers 902, 904 is controlled by a word clock signal 916provided by a circuit 914 that divides the half-rate symbol clock signal910 by seven. Input timing of the serializers 906, 908 is controlled bythe word clock signal 916 and output timing of the serializers 906, 908is controlled by the half-rate symbol clock signal 910.

In one example, the first mapping circuit 900 provides FRP symbols tothe even symbol path 918 that encode a 16-bit word that is differentfrom the 16-bit word encoded in FRP symbols provided to the odd symbolpath 920. For example, FRP symbol N is provided to the even symbol path918 and symbol N+1 is provided to the odd symbol path 920, where symbolN+1 follows symbol N in transmission. The sequences obtained from thetwo mappers 902, 904 may be provided in turn to the even and odd symbolpaths 918, 920, effectively combining the two sequences of 7 FRP symbolsinto a 14-symbol sequence.

In another example, each of the two mappers 902, 904 may be configuredas an even mapper 902 and an odd mapper 904, both mappers 902, 904 beingconfigured to receive the same 32-bit word. In this example, the evenmapper 902 provides the even symbols in the 14-symbol sequence thatrepresents the 32-bit word, while the odd mapper 904 provides the oddsymbols in the 14-symbol sequence that represents the 32-bit word.Symbols produced by the mappers 902, 904 can be serialized and providedto the corresponding symbol path. 918, 920. In this example, signalingon the serial bus is consistent with conventional C-PHY transmitters.

The second mapping circuit 930 uses a single mapper 934 and isconfigured to receive data in 16-bit words. The single mapper 934 isconfigured to encode each 16-bit word in a sequence of 7 FRP symbols.The sequence of 7 FRP symbols may be loaded into a 7-to-2 shift register938 using a demultiplexer 936 that provides the even and odd symbols toshift registers coupled to the corresponding even and odd symbol paths918, 920. The demultiplexer 936 is clocked at half the input data clockrate, using a clock signal 942 derived from the symbol clock signal 910through the operation of a divider 940.

FIG. 10 illustrates a first example of a transmitter 1000 configured touse a half-rate symbol clock signal 910 to encode input data 1020 insymbols that control signaling state of a C-PHY trio 1024. Thetransmitter 1000 is implemented with an even symbol path and an oddsymbol path, where each even symbol defines a signaling state that isimmediately followed by a signaling state defined by an odd symbol andeach odd symbol defines a signaling state that is immediately followedby a signaling state defined by an even symbol. In some implementations,the resultant sequence of symbols complies with C-PHY protocols. FIG. 11illustrates timing 1100 for the transmitter 1000.

The input data 1020 may be received by a mapping circuit 1002 as two16-bit words or as a single 32-bit word. The mapping circuit 1002 maycorrespond to one of the mapping circuits 900, 930 illustrated in FIG.9, for example. Each symbol in the sequence of FRP symbols provided bythe mapping circuit 1002 is captured by one of the flipflops 1004 and1014 that maintain the next FRP symbols 1030, 1032 to be encoded fortransmission. For each cycle of the half-rate symbol clock signal 910,the flipflop 1004 in the even symbol path provides the input to a firstwire state encoder 1006, and the flipflop 1014 in the odd symbol pathprovides the input to a second wire state encoder 1016.

The first wire state encoder 1006 provides, as its output, a next even3-bit wire state symbol 1034 to define signaling state of each wire ofthe C-PHY trio 1024. The next even 3-bit wire state symbol 1034 isgenerated based on differences between the even 3-bit symbol 1030 andthe current odd 3-bit wire state symbol 1040 generated on the odd symbolpath. A flipflop 1008 clocked by an inverse of the half-rate symbolclock signal 910 provides the current even 3-bit wire state symbol 1038by capturing the next even 3-bit wire state symbol 1034 when it isclocked through flipflop 1008 in order to be transmitted.

The second wire state encoder 1016 provides, as its output, a next odd3-bit wire state symbol 1036 to define signaling state of each wire ofthe C-PHY trio 1024. The next odd 3-bit wire state symbol 1036 isgenerated based on differences between the odd 3-bit symbol 1032 and thecurrent even 3-bit wire state symbol 1038 generated on the even symbolpath. A flipflop 1018 clocked by the half-rate symbol clock signal 910provides the current odd 3-bit wire state symbol 1040 by capturing thenext odd 3-bit wire state symbol 1036 when it is clocked throughflipflop 1018 in order to be transmitted.

A multiplexer 1010 selects its output 1042 from the current even 3-bitwire state symbol 1038 and the current odd 3-bit wire state symbol 1040.The output 1042 of the multiplexer 1010 is provided to a pre-drive andcontrol circuit 1012 that controls a set of line drivers 1022 coupled tothe C-PHY trio 1024. The multiplexer 1010 is controlled by the half-ratesymbol clock signal 910, such that even and odd symbols control thestate of the 1002 in different phases (half-cycles) of the half-ratesymbol clock signal 910.

FIG. 12 illustrates a second example of a transmitter 1200 configured touse a half-rate symbol clock signal 910 to encode input data 1220 insymbols that control signaling state of a C-PHY trio 1242. Thetransmitter 1200 operates in a similar fashion to the transmitter 1000of FIG. 10 with added pipeline circuits 1226, 1236 that supportequalization.

The transmitter 1200 is implemented with an even symbol path and an oddsymbol path, where each even symbol defines a signaling state that isimmediately followed by a signaling state defined by an odd symbol andeach odd symbol defines a signaling state that is immediately followedby a signaling state defined by an even symbol. The resultant sequenceof symbols complies with C-PHY protocols.

The input data 1220 may be received by a mapping circuit 1202 as two16-bit words or as a single 32-bit word. The mapping circuit 1202 maycorrespond to one of the mapping circuits 900, 930 illustrated in FIG.9, for example. Each symbol in the sequence of FRP symbols provided bythe mapping circuit 1202 is captured by one of the flipflops 1204 and1214 that maintain the next FRP symbols for processing. For each cycleof the half-rate symbol clock signal 910, the flipflop 1204 in the evensymbol path provides the input to a first wire state encoder 1206, andthe flipflop 1214 in the odd symbol path provides the input to a secondwire state encoder 1216.

The first wire state encoder 1206 provides, as its output, a next even3-bit wire state symbol to define signaling state of each wire of theC-PHY trio 1242. The next even 3-bit wire state symbol is generatedbased on differences between the next even FRP symbol and the currentodd 3-bit wire state symbol 1246 generated on the odd symbol path. Aflipflop 1208 clocked by an inverse of the half-rate symbol clock signal910 provides the current even 3-bit wire state symbol 1244 by capturingthe next even 3-bit wire state symbol provided by the first wire stateencoder 1206 when it is clocked through flipflop 1208 in order to betransmitted.

The second wire state encoder 1216 provides, as its output, a next odd3-bit wire state symbol to define signaling state of each wire of theC-PHY trio 1242. The next odd 3-bit wire state symbol is generated basedon differences between the next odd FRP symbol and the current even3-bit wire state symbol 1244 generated on the even symbol path. Aflipflop 1218 clocked by the half-rate symbol clock signal 910 providesthe current odd 3-bit wire state symbol 1246 by capturing the next odd3-bit wire state symbol provided by the second wire state encoder 1216when it is clocked through flipflop 1218 in order to be transmitted.

In the illustrated example, the current even 3-bit wire state symbol1244 and the current odd 3-bit wire state symbol 1246 are provided torespective even and odd pre-drive and control circuits 1222, 1232 thatproduce one or more driver control signals 1224, 1234 configured tocontrol a set of line drivers 1210 coupled to the C-PHY trio 1242. Thedriver control signals 1224, 1234 are provided to respective pipelinecircuits 1226, 1236 that provide a delay sufficient to enableequalization circuits 1228, 1238 to determine an equalizationconfiguration for the driver control signals 1224, 1234. In theillustrated example, the pipeline circuits 1226, 1236 include two ormore flipflops that delay the driver control signals 1224, 1234 by acorresponding two or more clock cycles. The flipflops in the pipelinecircuit 1226 for the even symbol path are clocked by the inverse of thehalf-rate symbol clock signal 910 and the flipflops in the pipelinecircuit 1236 for the odd symbol path are clocked by the half-rate symbolclock signal 910 to maintain the timing relationship established betweenthe even and odd symbol paths. The delayed driver control signals areprovided by respective pipeline circuits 1226, 1236 to equalizercircuits 1228, 1238 that may apply a timing adjustment to certain of thedelayed driver control signals, generate driver amplitude controlsignals for certain of the delayed driver control signals, or providesome combination of timing and amplitude adjustments. The equalizercircuits 1228, 1238 provide the delayed driver control signals and/ortiming and amplitude adjustment control signals to the multiplexer 1240.

The multiplexer 1240 selects between the outputs of the equalizercircuits 1228, 1238 to provide its output. The output of the multiplexer1240 is provided to the set of line drivers 1210 coupled to the C-PHYtrio 1242. The multiplexer 1240 is controlled by the half-rate symbolclock signal 910, such that even and odd symbols control the state ofthe C-PHY trio 1242 in different phases (half-cycles) of the half-ratesymbol clock signal 910.

A receiver configured to decode sequences of symbols transmitted inaccordance with timing provided by a half-rate symbol clock signal maybe configured with separate even and odd symbol paths. Difference signalprocessors may be employed to demultiplex the difference signals toobtain current and previous wire states.

FIG. 13 illustrates one example of difference signal processors 1300,1330 and 1360 that may be used in a receiver configured for half-ratesymbol clock operation in accordance with certain aspects of thisdisclosure.

An AB difference signal processor 1300 receives the AB difference signal1302 from a comparator or line receiver circuit. The AB differencesignal 1302 may be received from one of a set of comparators such as theset of comparators 802 illustrated in FIG. 8. The comparators provide aset of difference signals {AB, BC, CA} representing the difference insignaling state of the trio of wires (referenced as wires A, B and C) ina C-PHY bus. In some implementations, the AB difference signal 1302 is amulti-bit signal and/or may be transmitted over two or more connectorsor wires. FIG. 15 is a timing diagram 1500 that includes a snapshot ofthe AB difference signal 1302, covering the signaling state for receivedsymbol intervals {N, N+1, . . . N+8}. The AB difference signal processor1300 includes a first flipflop 1304 that is clocked by the half-ratesymbol clock signal 1324 and configured to capture even AB state 1320,including AB state for each of the set of symbols {N−1, N+1, N+3, N+5and N+7}.

The AB difference signal processor 1300 includes a second flipflop 1306that is clocked by an inverse of the half-rate symbol clock signal 1324and configured to capture odd AB states 1322, including state for eachof the set of symbols {N, N+2, N+4 and N+6}. The AB difference signalprocessor 1300 also includes third and fourth flipflops 1308, 1310 thatare clocked by the half-rate symbol clock signal 1324 and that providealigned current even AB states 1314 and current odd AB states 1316. TheAB difference signal processor 1300 also includes a fifth flipflop 1312that is clocked by the half-rate symbol clock signal 1324 and thatcaptures current odd AB states 1316 to provide previous odd AB states1318 aligned in time with corresponding current even AB states 1314 andcurrent odd AB states 1316.

A BC difference signal processor 1330 receives the BC difference signal1332 from a comparator or line receiver circuit. The BC differencesignal 1332 may be received from one of a set of comparators such as theset of comparators 802 illustrated in FIG. 8. In some implementations,the BC difference signal 1332 is a multi-bit signal and/or may betransmitted over two or more connectors or wires. The BC differencesignal processor 1330 includes a first flipflop 1334 that is clocked bythe half-rate symbol clock signal 1324 and configured to capture even BCstate 1350, including BC state for each of the set of symbols {N−1, N+1,N+3, N+5 and N+7}.

The BC difference signal processor 1330 includes a second flipflop 1336that is clocked by an inverse of the half-rate symbol clock signal 1324and configured to capture odd BC states 1352, including state for eachof the set of symbols {N, N+2, N+4 and N+6}. The BC difference signalprocessor 1330 also includes third and fourth flipflops 1338, 1340 thatare clocked by the half-rate symbol clock signal 1324 and that providealigned current even BC states 1344 and current odd BC states 1346. TheBC difference signal processor 1330 also includes a fifth flipflop 1342that is clocked by the half-rate symbol clock signal 1324 and thatcaptures current odd BC states 1346 to provide previous odd BC states1348 aligned in time with corresponding current even BC states 1344 andcurrent odd BC states 1346.

A CA difference signal processor 1360 receives the CA difference signal1362 from a comparator or line receiver circuit. The CA differencesignal 1362 may be received from one of a set of comparators such as theset of comparators 802 illustrated in FIG. 8. In some implementations,the CA difference signal 1362 is a multi-bit signal and/or may betransmitted over two or more connectors or wires. The CA differencesignal processor 1360 includes a first flipflop 1364 that is clocked bythe half-rate symbol clock signal 1324 and configured to capture even CAstate 1380, including CA state for each of the set of symbols {N−1, N+1,N+3, N+5 and N+7}.

The CA difference signal processor 1360 includes a second flipflop 1366that is clocked by an inverse of the half-rate symbol clock signal 1324and configured to capture odd CA states 1382, including state for eachof the set of symbols {N, N+2, N+4 and N+6}. The CA difference signalprocessor 1360 also includes third and fourth flipflops 1368, 1370 thatare clocked by the half-rate symbol clock signal 1324 and that providealigned current even CA states 1374 and current odd CA states 1376. TheCA difference signal processor 1360 also includes a fifth flipflop 1372that is clocked by the half-rate symbol clock signal 1324 and thatcaptures current odd CA states 1376 to provide previous odd CA states1378 aligned in time with corresponding current even CA states 1374 andcurrent odd CA states 1376.

FIG. 14 illustrates a receiver circuit 1400 configured to use ahalf-rate symbol clock signal 1324 to decode data 1450 from signalingstate of a C-PHY bus. The receiver circuit 1400 is implemented with aneven symbol path and an odd symbol path, where each symbol correspondsto data encoded in transitions between successive signaling states. Eacheven symbol represents a first signaling state that is immediatelyfollowed by a second signaling state represented by an odd symbol andeach odd symbol represents a third signaling state that is immediatelyfollowed by a fourth signaling state represented by an even symbol. Thesequence of symbols complies with C-PHY protocols. FIG. 15 illustratestiming associated with the receiver circuit 1400.

The receiver circuit 1400 may include or may be coupled to comparatorssuch as the set of comparators 802 illustrated in FIG. 8. Thecomparators provide a set of difference signals {AB, BC, CA}representing the difference in signaling state of the trio of wires(referenced as wires A, B and C) in a C-PHY bus. Three difference signalprocessors 1402, 1404, 1406 are provided to extract information fromsignaling states in a sequence of symbol transmission intervals on theC-PHY bus. The symbol transmission interval is defined by the symboltransmission rate. The set of difference signals is also provided to aclock recovery circuit 1430 that generates the half-rate symbol clocksignal 1324. Each period of the half-rate symbol clock signal 1324defines two symbol transmission intervals.

The AB difference signal processor 1402 provides the current even ABstates, the current odd AB states and the previous odd AB states to apair of wire state decoders. The BC difference signal processor 1404provides the current even BC states, the current odd BC states and theprevious odd BC states to a pair of wire state decoders. The CAdifference signal processor 1406 provides the current even CA states,the current odd CA states and the previous odd CA states to a pair ofwire state decoders.

An even wire state decoder 1408 provides 3-bit even FRP symbols 1436 bydetermining differences between the current odd states 1412 for the AB,BC and CA difference signals and the current even states 1414 for theAB, BC and CA difference signals. The current even states 1414 for theAB, BC and CA difference signals occur before the current odd states1412 for the AB, BC and CA. An odd wire state decoder 1410 provides3-bit odd FRP symbols 1438 by determining differences between thecurrent even states 1414 for the AB, BC and CA difference signals andthe previous odd states 1416 for the AB, BC and CA difference signals.The previous odd states 1416 for the AB, BC and CA difference signalsoccur before the current even states 1414 for the AB, BC and CA.

The even FRP symbols 1436 and the odd FRP symbols 1438 are held incorresponding registers or flipflops 1418 and 1420 respectively toprovide even FRP input 1440 and odd FRP input 1442 to 1-to-7serial-to-parallel converters 1422, 1424. The registers or flipflops1418 and 1420 and the inputs of the serial-to-parallel converters 1422,1424 are clocked by the half-rate symbol clock signal 1324. Theserial-to-parallel converters 1422, 1424 provide 21-bit representationsof sequences of symbols as even and odd inputs 1444 to a demapper 1426based on timing provided by a data clock signal 1434 provided by acircuit 1428 that divides the half-rate symbol clock signal 1324 byseven. The demapper 1426 interleaves and decodes the even and odd inputs1444 to obtain decoded data 1450, which may be output in 16-bit or32-bit words. The serial-to-parallel converters 1422, 1424 and thedemapper 1426 may operate based on timing provided by the data clocksignal 1434.

FIG. 16 illustrates examples of demapping circuits 1600, 1630 that maybe implemented in C-PHY receivers that are configured with a dual patharchitecture in accordance aspects of the disclosure. The firstdemapping circuit 1600 includes two demappers 1606, 1608. A firstdeserializer 1602, or serial to parallel convertor, provides the firstdemapper 1606 with a 21-bit representation of each sequence of seven3-bit symbols received from the even symbol path 1612. A seconddeserializer 1604 provides the second demapper 1608 with a 21-bitrepresentation of each sequence of seven 3-bit symbols received from theodd symbol path 1614. The symbols received from the even symbol path1612 and the odd symbol path 1614 may be configured as FRP symbols. Thedemappers 1606, 1608 may be configured to convert the 7-symbol sequencesinto data in accordance with C-PHY encoding. In some implementations,each of the demappers 1606, 1608 may decode a sequence of seven symbolsby indexing a lookup table using the 21-bit representation of thesequence of seven symbols. In one example, the first demapping circuit1600 may provide output data 1620 as two 16-bit words. In anotherexample, the first demapping circuit 1600 may provide output data 1620as two 16-bit words. or as a single 32-bit word.

The deserializers 1602, 1604 receive one symbol per clock cycle of ahalf-rate symbol clock signal 1610, which has a frequency equal to halfthe desired symbol transmission rate. In the illustrated example, eachof the two demappers 1606, 1608 receive a set of seven 3-bit FRP symbolsfrom corresponding deserializers 1602, 1604. Timing of the operation ofthe demappers 1606, 1608 and the output of the deserializers 1602, 1604is controlled by a word clock signal 1618 provided by a circuit 1616that divides the half-rate symbol clock signal 1610 by seven. In theillustrated example, FRP symbol N is received from the even symbol path1612 and symbol N+1 is received from the odd symbol path 1614, wheresymbol N+1 is received from the C-PHY bus after symbol N.

In some implementations, each of the two demappers 1606, 1608 may beconfigured as an even demapper 1606 and an odd demapper 1608, bothdemappers 1606, 1608 being configured to output parts of the same 32-bitword. In some implementations, signaling on the serial bus is consistentwith conventional C-PHY transmitters.

The second demapping circuit 1630 uses a single demapper 1642 and isconfigured to interleave symbols received from the even symbol path 1652and the odd symbol path 1654. In one example, the sequences of 7 FRPsymbols are captured from deserializers 1632, 1634 by sets of flipflops1636, 1638, where the sets of flipflops 1636, 1638 and the outputs ofthe deserializers 1632, 1634 are controlled by a word clock signal 1656,which may be obtained from a divider 1646 that divides the half-ratesymbol clock signal 1610 by 7. In one example, the deserializers 1632,1634 are configured to assemble up to 7 received symbols into a sequenceof symbols captured by respective sets of flipflops 1636, 1638. A firstset of flipflops 1636 captures 7-symbol sequences from the even symbolpath 1652 and a second set of flipflops 1638 captures 7-symbol sequencesfrom the odd symbol path 1654. A multiplexer 1640 feeds the demapper1642 in accordance with a select signal provided by a half-word clocksignal 1658, which may be obtained from a divider 1648 that divides thehalf-rate symbol clock signal 1610 by 3.5. The demapper 1642 producestwo 16-bit data words at an output 1650 of the second demapping circuit1630 for every cycle of the half-rate symbol clock signal 1610. In oneexample, a first 16-bit data word is decoded from a 7-symbol sequenceprocessed through the even symbol path 1652 and a second 16-bit dataword is decoded from a 7-symbol sequence processed through the oddsymbol path 1654.

Examples of Processing Circuits and Methods

FIG. 17 is a conceptual diagram 1700 illustrating an example of ahardware implementation for an apparatus employing a processing circuit1702 that may be configured to perform one or more functions disclosedherein. In accordance with various aspects of the disclosure, anelement, or any portion of an element, or any combination of elements asdisclosed herein may be implemented using the processing circuit 1702.The processing circuit 1702 may include certain devices, circuits,and/or logic that support the various encoding schemes disclosed herein.In one example, the processing circuit 1702 may include some combinationof circuitry and modules that facilitates the encoding of data intosymbols, and line drivers that are adapted to assert three or morevoltage levels on the wires of a serial bus. In another example, theprocessing circuit 1702 may include some combination of circuitry andmodules that facilitates the encoding of data into symbols using 3-phaseencoders, mappers, drivers and/or equalizers. The processing circuit1702 may include a state machine or another type of processing devicethat manages encoding and/or decoding processes as disclosed herein.

The processing circuit 1702 may include one or more processors 1704 thatare controlled by some combination of hardware and software modules.Examples of processors 1704 include microprocessors, microcontrollers,digital signal processors (DSPs), field programmable gate arrays(FPGAs), programmable logic devices (PLDs), state machines, sequencers,gated logic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. The one or more processors 1704 may include specializedprocessors that perform specific functions, and that may be configured,augmented or controlled by one of the software modules 1716. The one ormore processors 1704 may be configured through a combination of softwaremodules 1716 loaded during initialization, and further configured byloading or unloading one or more software modules 1716 during operation.

In the illustrated example, the processing circuit 1702 may beimplemented with a bus architecture, represented generally by the bus1710. The bus 1710 may include any number of interconnecting buses andbridges depending on the specific application of the processing circuit1702 and the overall design constraints. The bus 1710 links togethervarious circuits including the one or more processors 1704, and aprocessor-readable storage medium 1706. The processor-readable storagemedium 1706 may include memory devices and mass storage devices and maybe referred to herein as computer-readable media and/orprocessor-readable media. The bus 1710 may also link various othercircuits such as timing sources, timers, peripherals, voltageregulators, and power management circuits. A bus interface 1708 mayprovide an interface between the bus 1710 and one or more transceivers1712. A transceiver 1712 may be provided for each networking technologysupported by the processing circuit. In some instances, multiplenetworking technologies may share some or all of the circuitry orprocessing modules found in a transceiver 1712. Each transceiver 1712provides a means for communicating with various other apparatus over atransmission medium. Depending upon the nature of the apparatus, a userinterface 1718 (e.g., keypad, display, speaker, microphone, joystick)may also be provided, and may be communicatively coupled to the bus 1710directly or through the bus interface 1708.

A processor 1704 may be responsible for managing the bus 1710 and forgeneral processing that may include the execution of software stored ina processor-readable medium that may include the processor-readablestorage medium 1706. In this respect, the processing circuit 1702,including the processor 1704, may be used to implement any of themethods, functions and techniques disclosed herein. Theprocessor-readable storage medium 1706 may be used for storing data thatis manipulated by the processor 1704 when executing software, and thesoftware may be configured to implement any one of the methods disclosedherein.

One or more processors 1704 in the processing circuit 1702 may executesoftware. Software shall be construed broadly to mean instructions,instruction sets, code, code segments, program code, programs,subprograms, software modules, applications, software applications,software packages, routines, subroutines, objects, executables, threadsof execution, procedures, functions, algorithms, etc., whether referredto as software, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. The software may reside in computer-readableform in the processor-readable storage medium 1706 or in another,external processor-readable medium. The processor-readable storagemedium 1706 may include a non-transitory processor-readable medium. Anon-transitory processor-readable medium includes, by way of example, amagnetic storage device (e.g., hard disk, floppy disk, magnetic strip),an optical disk (e.g., a compact disc (CD) or a digital versatile disc(DVD)), a smart card, a flash memory device (e.g., a “flash drive,” acard, a stick, or a key drive), a random access memory (RAM), a ROM, aPROM, an erasable PROM (EPROM), an EEPROM, a register, a removable disk,and any other suitable medium for storing software and/or instructionsthat may be accessed and read by a computer. The processor-readablestorage medium 1706 may also include, by way of example, a carrier wave,a transmission line, and any other suitable medium for transmittingsoftware and/or instructions that may be accessed and read by acomputer. Processor-readable storage medium 1706 may reside in theprocessing circuit 1702, in the processor 1704, external to theprocessing circuit 1702, or be distributed across multiple entitiesincluding the processing circuit 1702. The processor-readable storagemedium 1706 may be embodied in a computer program product. By way ofexample, a computer program product may include a processor-readablemedium in packaging materials. Those skilled in the art will recognizehow best to implement the described functionality presented throughoutthis disclosure depending on the particular application and the overalldesign constraints imposed on the overall system.

The processor-readable storage medium 1706 may maintain softwaremaintained and/or organized in loadable code segments, modules,applications, programs, etc., which may be referred to herein assoftware modules 1716. Each of the software modules 1716 may includeinstructions and data that, when installed or loaded on the processingcircuit 1702 and executed by the one or more processors 1704, contributeto a run-time image 1714 that controls the operation of the one or moreprocessors 1704. When executed, certain instructions may cause theprocessing circuit 1702 to perform functions in accordance with certainmethods, algorithms and processes described herein.

Some of the software modules 1716 may be loaded during initialization ofthe processing circuit 1702, and these software modules 1716 mayconfigure the processing circuit 1702 to enable performance of thevarious functions disclosed herein. For example, some software modules1716 may configure internal devices and/or logic circuits 1722 of theprocessor 1704 and may manage access to external devices such as thetransceiver 1712, the bus interface 1708, the user interface 1718,timers, mathematical coprocessors, and so on. The software modules 1716may include a control program and/or an operating system that interactswith interrupt handlers and device drivers, and that controls access tovarious resources provided by the processing circuit 1702. The resourcesmay include memory, processing time, access to the transceiver 1712, theuser interface 1718, and so on.

One or more processors 1704 of the processing circuit 1702 may bemultifunctional, whereby some of the software modules 1716 are loadedand configured to perform different functions or different instances ofthe same function. The one or more processors 1704 may additionally beadapted to manage background tasks initiated in response to inputs fromthe user interface 1718, the transceiver 1712, and device drivers, forexample. To support the performance of multiple functions, the one ormore processors 1704 may be configured to provide a multitaskingenvironment, whereby each of a plurality of functions is implemented asa set of tasks serviced by the one or more processors 1704 as needed ordesired. In one example, the multitasking environment may be implementedusing a timesharing program 1720 that passes control of a processor 1704between different tasks, whereby each task returns control of the one ormore processors 1704 to the timesharing program 1720 upon completion ofany outstanding operations and/or in response to an input such as aninterrupt. When a task has control of the one or more processors 1704,the processing circuit is effectively specialized for the purposesaddressed by the function associated with the controlling task. Thetimesharing program 1720 may include an operating system, a main loopthat transfers control on a round-robin basis, a function that allocatescontrol of the one or more processors 1704 in accordance with aprioritization of the functions, and/or an interrupt driven main loopthat responds to external events by providing control of the one or moreprocessors 1704 to a handling function.

FIG. 18 is a flow chart 1800 of a data communication method that may beperformed at a transmitter coupled to a multi-wire communication link.In one example, the communication link may have three wires and data maybe encoded in phase state and amplitude of a signal transmitted indifferent phases on each of the three wires. The method may beperformed, at least in part, at the transmitter 1000 or 1200 illustratedin FIGS. 10 and 12 respectively.

At block 1802, the transmitter 1000 or 1200 may configure a plurality ofline drivers to couple the apparatus to a 3-wire link. At block 1804,the transmitter 1000 or 1200 may receive a first symbol in a sequence ofsymbols at a first wire state encoder when the 3-wire link is in a firstsignaling state. At block 1806, the transmitter 1000 or 1200 may definea second signaling state for the 3-wire link based on the first symboland the first signaling state. At block 1808, the transmitter 1000 or1200 may receive a second symbol in the sequence of symbols at a secondwire state encoder. At block 1810, the transmitter 1000 or 1200 maydefine a third signaling state for the 3-wire link based on the secondsymbol and the second signaling state. The first symbol may immediatelyprecede the second symbol in the sequence of symbols. The 3-wire linktransitions from the first signaling state to the second signaling stateand from the second signaling state to the third signaling state inconsecutive symbol transmission intervals. Signaling states of at leastone wire in the 3-wire link changes when the 3-wire link transitionsfrom the second signaling state to the third signaling state.

In one example, each of the first wire state encoder and the second wirestate encoder defines signaling states for the 3-wire link every twosymbol transmission intervals.

In certain examples, a half-rate symbol clock signal that has a periodtwice the duration of each symbol transmission interval may be provided.The transmitter 1000 or 1200 may select between the second signalingstate and the third signaling state to provide wire state information toa driver control circuit that controls the plurality of line drivers.Selection may be based on phase of the half-rate symbol clock signal.The transmitter 1000 or 1200 may clock first flipflops clocked using aninverse of the half-rate symbol clock signal. The first flipflops may beconfigured to capture first control signals representative of the secondsignaling state. The transmitter 1000 or 1200 may clock second flipflopsusing the half-rate symbol clock signal. The second flipflops may beconfigured to capture second control signals representative of the thirdsignaling state. The transmitter 1000 or 1200 may provide the firstcontrol signals or the second control signals as the wire stateinformation. The transmitter 1000 or 1200 may map at least 16 bits ofdata to at least 7 symbols in the sequence of symbols. The 3-wire linkmay be operated in accordance with a C-PHY protocol.

In some implementations, the transmitter 1000 or 1200 may configure theplurality of line drivers when initiating transmission of the thirdsignaling state based on differences between the second signaling stateand the third signaling state.

FIG. 19 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1900 employing a processing circuit1902. The processing circuit 1902 typically has a processor 1916, whichmay be a microprocessor, microcontroller, digital signal processor, asequencer or a state machine. The processing circuit 1902 may beimplemented with a bus architecture, represented generally by the bus1910. The bus 1910 may include any number of interconnecting buses andbridges depending on the specific application of the processing circuit1902 and the overall design constraints. The bus 1910 links togethervarious circuits including one or more processors and/or hardwaremodules, represented by the processor 1916, the modules or circuits1904, 1906 and 1908, line drivers 1912 that are configured to drive thewires of a 3-wire link 1920, and the processor-readable storage medium1918. The bus 1910 may also link various other circuits such as timingsources, peripherals, voltage regulators, and power management circuits,which are well known in the art, and therefore, will not be describedany further.

The processor 1916 is responsible for general processing, including theexecution of software stored on the processor-readable storage medium1918. The software, when executed by the processor 1916, causes theprocessing circuit 1902 to perform the various functions described suprafor any particular apparatus. The processor-readable storage medium 1918may include transitory and/or non-transitory media, which may be usedfor storing data that is manipulated by the processor 1916 whenexecuting software, including symbol tables and intermediate indicesused to access the symbol tables. The processing circuit 1902 furtherincludes at least one of the modules 1904, 1906 and 1908. The modules1904, 1906 and 1908 may be implemented as software modules running inthe processor 1916, resident/stored in the processor-readable storagemedium 1918, one or more hardware modules coupled to the processor 1916,or some combination thereof. The modules 1904, 1906 and/or 1908 mayinclude microcontroller instructions, state machine configurationparameters, or some combination thereof.

In one configuration, the apparatus 1900 may be configured for datacommunication over a multi-wire interface. The apparatus 1900 mayinclude symbol mapping modules and/or circuits 1908 configured to encodedata in odd and even symbols using 3-phase encoding. The apparatus 1900may include symbol multiplexing modules and/or circuits 1906 configuredto merge or interleave the odd and even symbols to obtain a sequence ofsymbols. The apparatus 1900 may include wire state encoding modulesand/or circuits 1904 that are configured to use the sequence of symbolsto cause the line drivers 1912 to configure the signaling state of the3-wire link 1920 during corresponding symbol transmission intervals. Inone example, the line drivers 1912 provide 7 or more signaling states oneach wire, and each wire is driven to a different signaling state thanthe other wires in the 3-wire link 1920.

In one example, the apparatus 1900 has a pair of wire state encoders andthe line drivers 1912 are configured to couple the apparatus to the3-wire link 1920. A first wire state encoder is configured to receive afirst symbol in a sequence of symbols when the 3-wire link 1920 is in afirst signaling state, and to define a second signaling state for the3-wire link based on the first symbol and the first signaling state. Thesecond wire state encoder is configured to receive a second symbol inthe sequence of symbols, and to define a third signaling state for the3-wire link based on the second symbol and the second signaling state.The first symbol immediately precedes the second symbol in the sequenceof symbols. The 3-wire link 1920 transitions from the first signalingstate to the second signaling state and from the second signaling stateto the third signaling state in consecutive symbol transmissionintervals. Signaling states of at least one wire in the 3-wire link 1920changes when the 3-wire link 1920 transitions from the second signalingstate to the third signaling state. In one example, each wire stateencoder defines signaling states for the 3-wire link 1920 every twosymbol transmission intervals.

In some implementations, the apparatus 1900 has a clock generationcircuit configured to provide a half-rate symbol clock signal that has aperiod twice the duration of each symbol transmission interval. Theapparatus may have a driver control circuit configured to control theline drivers 1912, and a multiplexer that selects between the secondsignaling state and the third signaling state to provide wire stateinformation to the driver control circuit. The multiplexer may selectbetween the second signaling state and the third signaling state basedon phase of the half-rate symbol clock signal. The apparatus 1900 mayfurther include first flipflops clocked by an inverse of the half-ratesymbol clock signal and configured to capture first control signalsrepresentative of the second signaling state, and second flipflopsclocked by the half-rate symbol clock signal and configured to capturesecond control signals representative of the third signaling state. Themultiplexer may be further configured to provide the first controlsignals or the second control signals as the wire state information.

In some implementations, the apparatus 1900 has one or more mappersconfigured to map at least 16 bits of data to at least 7 symbols in thesequence of symbols. The 3-wire link 1620 may be operated in accordancewith a C-PHY protocol.

In some implementations the apparatus 1900 has an equalizer circuitconfigured to receive delayed versions of the second signaling state andthe third signaling state, and to configure the plurality of linedrivers when initiating transmission of the third signaling state basedon differences between the second signaling state and the thirdsignaling state.

The processor-readable storage medium 1918 may store instructions andother information related to the method illustrated in FIG. 18. Forexample, the processor-readable storage medium 1918 may includeinstructions that cause the processing circuit 1902 to configure theline drivers 1912 to couple the apparatus to the 3-wire link 1920,receive a first symbol in a sequence of symbols at a first wire stateencoder when the 3-wire link 1920 is in a first signaling state, definea second signaling state for the 3-wire link 1920 based on the firstsymbol and the first signaling state, receive a second symbol in thesequence of symbols at a second wire state encoder, and define a thirdsignaling state for the 3-wire link based on the second symbol and thesecond signaling state. The first symbol immediately precedes the secondsymbol in the sequence of symbols. The 3-wire link 1920 transitions fromthe first signaling state to the second signaling state and from thesecond signaling state to the third signaling state in consecutivesymbol transmission intervals. Signaling states of at least one wire inthe 3-wire link 1920 may change when the 3-wire link 1920 transitionsfrom the second signaling state to the third signaling state.

In some instances, each of the first wire state encoder and the secondwire state encoder defines signaling states for the 3-wire link 1920every two symbol transmission intervals.

In some implementations, the processor-readable storage medium 1918includes instructions that cause the processing circuit 1902 to providea half-rate symbol clock signal that has a period twice the duration ofeach symbol transmission interval. The processor-readable storage medium1918 may include instructions that cause the processing circuit 1902 toselect between the second signaling state and the third signaling stateto provide wire state information to a driver control circuit thatcontrols the plurality of line drivers. Selection may be based on phaseof the half-rate symbol clock signal. The processor-readable storagemedium 1918 may include instructions that cause the processing circuit1902 to clock first flipflops clocked using an inverse of the half-ratesymbol clock signal, where the first flipflops are configured to capturefirst control signals representative of the second signaling state. Theprocessor-readable storage medium 1918 may include instructions thatcause the processing circuit 1902 to clock second flipflops using thehalf-rate symbol clock signal, where the second flipflops are configuredto capture second control signals representative of the third signalingstate, and provide the first control signals or the second controlsignals as the wire state information.

The processor-readable storage medium 1918 may include instructions thatcause the processing circuit 1902 to map at least 16 bits of data to atleast 7 symbols in the sequence of symbols. The 3-wire link 1920 may beoperated in accordance with a C-PHY protocol. The processor-readablestorage medium 1918 may include instructions that cause the processingcircuit 1902 to configure the plurality of line drivers when initiatingtransmission of the third signaling state based on differences betweenthe second signaling state and the third signaling state.

FIG. 20 is a flow chart 2000 of a data communication method that may beperformed at a receiver coupled to a multi-wire communication link. Inone example, data may be encoded in phase state and amplitude of asignal transmitted in different phases on each of the three wires in a3-wire link 1920. The method may be performed, at least in part, at thereceiver circuit 1400 illustrated in FIG. 14.

At block 2002, the receiver circuit 1400 may provide difference signalsrepresentative of differences in signaling state between each pair ofwires in the 3-wire link 1920. At block 2004, the receiver circuit 1400may provide a first symbol based on differences between state of thedifference signals in a first half-cycle of a symbol clock and state ofthe difference signals in a second half-cycle of the symbol clock thatimmediately precedes the first half-cycle in the symbol clock. At block2006, the receiver circuit 1400 may provide a second symbol based ondifferences between the state of the difference signals in the secondhalf-cycle of the symbol clock and state of the difference signals in athird half-cycle of the symbol clock that immediately precedes thesecond half-cycle in the symbol clock. At block 2008, the receivercircuit 1400 may decode data from a sequence of symbols that includesthe first symbol and the second symbol. The first symbol immediatelyprecedes the second symbol in the sequence of symbols.

In various examples, the signaling state of at least one differencesignal changes at each transition between half-cycles of the half-ratesymbol clock. The method may include deriving the symbol clock from thedifference signals. The 3-wire link 1920 is operated in accordance witha C-PHY protocol. The method may include providing, for each differencesignal, a first signal representing the state of the correspondingdifference signal in the first half-cycle of the symbol clock, a secondsignal representing the state of the corresponding difference signal inthe second half-cycle of the symbol clock, and a third signalrepresenting the state of the corresponding difference signal in thethird half-cycle of the symbol clock. The method may include decoding a16-bit word from each of a plurality of sequences of seven symbols ordecoding a 32-bit word from each pair of sequences of seven symbolsgenerated concurrently by the first wire state decoder and the secondwire state decoder.

FIG. 21 is a diagram illustrating an example of a hardwareimplementation for an apparatus 2100 employing a processing circuit2102. The processing circuit 2102 typically has a processor 2116, whichmay be a microprocessor, microcontroller, digital signal processor, asequencer or a state machine. The processing circuit 2102 may beimplemented with a bus architecture, represented generally by the bus2110. The bus 2110 may include any number of interconnecting buses andbridges depending on the specific application of the processing circuit2102 and the overall design constraints. The bus 2110 links togethervarious circuits including one or more processors and/or hardwaremodules, represented by the processor 2116, the modules or circuits2104, 2106 and 2108, receivers 2112 that are configured to drive thewires of a 3-wire link 2120, and the processor-readable storage medium2118. The bus 2110 may also link various other circuits such as timingsources, peripherals, voltage regulators, and power management circuits,which are well known in the art, and therefore, will not be describedany further.

The processor 2116 is responsible for general processing, including theexecution of software stored on the processor-readable storage medium2118. The software, when executed by the processor 2116, causes theprocessing circuit 2102 to perform the various functions described suprafor any particular apparatus. The processor-readable storage medium 2118may include transitory and/or non-transitory media, which may be usedfor storing data that is manipulated by the processor 2116 whenexecuting software, including symbol tables and intermediate indicesused to access the symbol tables. The processing circuit 2102 furtherincludes at least one of the modules 2104, 2106 and 2108. The modules2104, 2106 and 2108 may be implemented as software modules running inthe processor 2116, resident/stored in the processor-readable storagemedium 2118, one or more hardware modules coupled to the processor 2116,or some combination thereof. The modules 2104, 2106 and/or 2108 mayinclude microcontroller instructions, state machine configurationparameters, or some combination thereof.

In one configuration, the apparatus 2100 may be configured for datacommunication over the 3-wire link 2120. The 3-wire link may be operatedin accordance with a C-PHY protocol. The apparatus 2100 may includedifference signal processing modules and/or circuits 2104 that areconfigured to determine differences in signaling state between pairs ofwires in the 3-wire link 2120. In one example, the receivers 2112determine differences between 7 or more signaling states on each wire.The apparatus 2100 may include wire state decoding modules and/orcircuits 2106 configured to produce odd and even symbols representativeof difference signals in each symbol transmission interval. Theapparatus 2100 may include symbol demapping modules and/or circuits 2108configured to decode data from the odd and even symbols.

In one example, the receivers 2112 are configured to provide differencesignals representative of differences in signaling state between eachpair of wires in the 3-wire link 2120, and the apparatus 2100 has afirst wire state decoder configured to provide a first symbol based ondifferences between state of the difference signals in a firsthalf-cycle of a symbol clock and state of the difference signals in asecond half-cycle of the symbol clock that immediately precedes thefirst half-cycle in the symbol clock, and a second wire state decoderconfigured to provide a second symbol based on differences between thestate of the difference signals in the second half-cycle of the symbolclock and state of the difference signals in a third half-cycle of thesymbol clock that immediately precedes the second half-cycle in thesymbol clock. The apparatus 2100 may have a demapper configured todecode data from a sequence of symbols that includes the first symboland the second symbol. The first symbol immediately precedes the secondsymbol in the sequence of symbols.

In some implementations, signaling state of at least one differencesignal changes at each transition between half-cycles of the half-ratesymbol clock. A clock recovery circuit may be configured to derive thesymbol clock from the difference signals.

In one example, the apparatus 2100 has a plurality of difference signalprocessors, each difference signal processor coupled to an associateddifference signal and configured to provide a first signal representingthe state of the corresponding difference signal in the first half-cycleof the symbol clock, a second signal representing the state of thecorresponding difference signal in the second half-cycle of the symbolclock, and a third signal representing the state of the correspondingdifference signal in the third half-cycle of the symbol clock.

In one example, the demapper is further configured to decode a 16-bitword from each of a plurality of sequences of seven symbols, or decode a32-bit word from each pair of sequences of seven symbols generatedconcurrently by the first wire state decoder and the second wire statedecoder.

The processor-readable storage medium 2118 may store instructions andother information related to the method illustrated in FIG. 20. Forexample, the processor-readable storage medium 2118 may includeinstructions that cause the processing circuit 2102 to providedifference signals representative of differences in signaling statebetween each pair of wires in a 3-wire link 2120, provide a first symbolbased on differences between state of the difference signals in a firsthalf-cycle of a symbol clock and state of the difference signals in asecond half-cycle of the symbol clock that immediately precedes thefirst half-cycle in the symbol clock, provide a second symbol based ondifferences between the state of the difference signals in the secondhalf-cycle of the symbol clock and state of the difference signals in athird half-cycle of the symbol clock that immediately precedes thesecond half-cycle in the symbol clock, and decode data from a sequenceof symbols that includes the first symbol and the second symbol. Thefirst symbol immediately precedes the second symbol in the sequence ofsymbols.

In some examples, signaling state of at least one difference signalchanges at each transition between half-cycles of the half-rate symbolclock. The storage medium 2118 may include instructions that cause theprocessing circuit 2102 to derive the symbol clock from the differencesignals. The 3-wire link 2120 may be operated in accordance with a C-PHYprotocol.

The storage medium 2118 may include instructions that cause theprocessing circuit 2102 to provide, for each difference signal, a firstsignal representing the state of the corresponding difference signal inthe first half-cycle of the symbol clock, a second signal representingthe state of the corresponding difference signal in the secondhalf-cycle of the symbol clock, and a third signal representing thestate of the corresponding difference signal in the third half-cycle ofthe symbol clock.

The storage medium 2118 may include instructions that cause theprocessing circuit 2102 to decode a 16-bit word from each of a pluralityof sequences of seven symbols, or decode a 32-bit word from each pair ofsequences of seven symbols generated concurrently by the first wirestate decoder and the second wire state decoder.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an illustration of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. Further, somesteps may be combined or omitted. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

1. A data communication apparatus, comprising: a plurality of receiversconfigured to provide difference signals representative of differencesin signaling state between each pair of wires in a 3-wire link; a firstwire state decoder configured to provide a first symbol representativeof differences between state of the difference signals in a firsthalf-cycle of a symbol clock and state of the difference signals in asecond half-cycle of the symbol clock that immediately precedes thefirst half-cycle in the symbol clock; a second wire state decoderconfigured to provide a second symbol representative of differencesbetween the state of the difference signals in the second half-cycle ofthe symbol clock and state of the difference signals in a thirdhalf-cycle of the symbol clock that immediately precedes the secondhalf-cycle in the symbol clock; and a demapper configured to decode datafrom a sequence of symbols that includes the first symbol and the secondsymbol, wherein the first symbol immediately precedes the second symbolin the sequence of symbols, wherein the demapper operates in accordancewith a word clock that is a double rate version of a half-rate wordclock used to capture the first symbol and the second symbol fromrespective deserializers.
 2. The data communication apparatus of claim 1further comprising: a multiplexer configured to feed the demapper inaccordance with state of the symbol clock.
 3. The data communicationapparatus of claim 1, further comprising: a clock recovery circuitconfigured to derive the symbol clock from the difference signals,wherein signaling state of at least one difference signal changes ateach transition between half-cycles of the symbol clock.
 4. The datacommunication apparatus of claim 1, further comprising: a plurality ofdifference signal processors, each difference signal processor coupledto an associated difference signal and configured to provide a firstsignal representing the state of a corresponding difference signal inthe first half-cycle of the symbol clock, a second signal representingthe state of a corresponding difference signal in the second half-cycleof the symbol clock, and a third signal representing the state of acorresponding difference signal in the third half-cycle of the symbolclock.
 5. The data communication apparatus of claim 1, wherein thedemapper is further configured to: decode a 16-bit word from each of aplurality of sequences of seven symbols.
 6. The data communicationapparatus of claim 1, wherein the demapper is further configured to:decode a 32-bit word from each pair of sequences of seven symbolsgenerated concurrently by the first wire state decoder and the secondwire state decoder.
 7. The data communication apparatus of claim 1,wherein the 3-wire link is operated in accordance with a C-PHY protocol.8. A data communication method, comprising: providing difference signalsrepresentative of differences in signaling state between each pair ofwires in a 3-wire link; providing a first symbol representative ofdifferences between state of the difference signals in a firsthalf-cycle of a symbol clock and state of the difference signals in asecond half-cycle of the symbol clock that immediately precedes thefirst half-cycle in the symbol clock; providing a second symbolrepresentative of differences between the state of the differencesignals in the second half-cycle of the symbol clock and state of thedifference signals in a third half-cycle of the symbol clock thatimmediately precedes the second half-cycle in the symbol clock;providing a sequence of symbols by selecting between the first symboland the second symbol in accordance with state of the symbol clock,wherein the first symbol immediately precedes the second symbol in thesequence of symbols; and decoding data from the sequence of symbols. 9.The data communication method of claim 8, wherein signaling state of atleast one difference signal changes at each transition betweenhalf-cycles of the symbol clock.
 10. The data communication method ofclaim 8, further comprising: deriving the symbol clock from thedifference signals, wherein the 3-wire link is operated in accordancewith a C-PHY protocol.
 11. The data communication method of claim 8,further comprising: for each difference signal, providing a first signalrepresenting the state of a corresponding difference signal in the firsthalf-cycle of the symbol clock, a second signal representing the stateof a corresponding difference signal in the second half-cycle of thesymbol clock, and a third signal representing the state of acorresponding difference signal in the third half-cycle of the symbolclock.
 12. The data communication method of claim 8, further comprising:decoding a 16-bit word from each of a plurality of sequences of sevensymbols.
 13. The data communication method of claim 8, furthercomprising: decoding a 32-bit word from each pair of sequences of sevensymbols generated concurrently by a first wire state decoder and asecond wire state decoder.
 14. A non-transitory processor-readablestorage medium comprising code for: providing difference signalsrepresentative of differences in signaling state between each pair ofwires in a 3-wire link; providing a first symbol representative ofdifferences between state of the difference signals in a firsthalf-cycle of a symbol clock and state of the difference signals in asecond half-cycle of the symbol clock that immediately precedes thefirst half-cycle in the symbol clock; providing a second symbolrepresentative of differences between the state of the differencesignals in the second half-cycle of the symbol clock and state of thedifference signals in a third half-cycle of the symbol clock thatimmediately precedes the second half-cycle in the symbol clock;providing a sequence of symbols by selecting between the first symboland the second symbol in accordance with state of the symbol clock,wherein the first symbol immediately precedes the second symbol in thesequence of symbols; and decoding data from the sequence of symbols. 15.The non-transitory processor-readable storage medium of claim 14,wherein signaling state of at least one difference signal changes ateach transition between half-cycles of the symbol clock.
 16. Thenon-transitory processor-readable storage medium of claim 14, furthercomprising code for: deriving the symbol clock from the differencesignals, wherein the 3-wire link is operated in accordance with a C-PHYprotocol.
 17. The non-transitory processor-readable storage medium ofclaim 14, further comprising code for: for each difference signal,providing a first signal representing the state of a correspondingdifference signal in the first half-cycle of the symbol clock, a secondsignal representing the state of a corresponding difference signal inthe second half-cycle of the symbol clock, and a third signalrepresenting the state of a corresponding difference signal in the thirdhalf-cycle of the symbol clock.
 18. The non-transitoryprocessor-readable storage medium of claim 14, further comprising codefor: decoding a 16-bit word from each of a plurality of sequences ofseven symbols.
 19. The non-transitory processor-readable storage mediumof claim 14, further comprising code for: decoding a 32-bit word fromeach pair of sequences of seven symbols generated concurrently by afirst wire state decoder and a second wire state decoder.
 20. Anapparatus comprising: means for providing difference signalsrepresentative of differences in signaling state between each pair ofwires in a 3-wire link; means for generating symbols using thedifference signals, including: a first wire state decoder configured togenerate a first symbol representative of differences between state ofthe difference signals in a first half-cycle of a symbol clock and stateof the difference signals in a second half-cycle of the symbol clockthat immediately precedes the first half-cycle in the symbol clock; anda second wire state decoder configured to generate a second symbolrepresentative of differences between the state of the differencesignals in the second half-cycle of the symbol clock and state of thedifference signals in a third half-cycle of the symbol clock thatimmediately precedes the second half-cycle in the symbol clock; meansfor providing a sequence of symbols by selecting between the firstsymbol and the second symbol in accordance with state of the symbolclock, wherein the first symbol immediately precedes the second symbolin the sequence of symbols; and means for decoding data from thesequence of symbols.